Eighty-eight adult patients with histologically verified cerebral low grade gliomas (grades 1 and 2) treated with post-operative radiotherapy at the Royal Marsden Hospital between 1960 and 1985 were reviewed. Survival of oligodendroglioma patients was greater than those with astrocytoma (64% vs 36% at 5 years) but the difference was less marked in the long term (35% vs 26% at 10 years). Previous studies have identified prognostic factors important in these tumors: age, extent of surgery, grade, performance status, and duration of symptoms. In this study of low grade astrocytomas and oligodendrogliomas, age (highly significant in the former and significant in the latter), extent of surgery (oligodendrogliomas), and performance status have been demonstrated as factors influencing outcome. The precise role of radiotherapy including the optimal radiation dose and timing of treatment remains unclear. The information, given by a retrospective analysis such as this, helps in the design of prospective, randomized studies looking at radiation dose and time of surgical and radiotherapeutic interventions, always with careful assessment needed of quality of life and treatment morbidity.